The invention relates to lightning arrester devices as primarily used on electrical power lines and equipment, and more particularly to an improved current interrupting lightning arrester isolator, the use of which avoids the starting of fires around rural power poles, while still giving a visual indication that the isolator has been activated.
When lightning strikes overhead power lines and equipment that are protected by lightning arresters, it is usually diverted to ground through the lightning arrester, which has a ground lead connected to a grounding electrode. However, when current flow through the lightning arrester is excessive, the line becomes grounded and it is necessary to disconnect the ground lead so that the normal operation of the line may be resumed. Therefore, isolators have been included on lightning arresters, for disconnecting the ground lead in the event of excessive current flow through the arrester.
A type of isolator which has been in common use prior to the present invention is an explosive disconnect, usually comprising a powder charge similar to that of a 0.22 caliber bullet, encapsulated in hard plastic material. Upon excessive current flow though the lightning arrester, the powder charge was ignited and a portion of the isolator, to which the ground lead was connected, would blow away from the lightning arrester. This provided a visual indication of the failure of the lightning arrester, but resulted in fragments of hot material being ejected upon isolation of the ground lead, and these hot fragments would often cause fires in the vicinity of the power pole or other equipment.
As a result, in California, for example, clearing of all flammable material is required within ten feet of rural power poles supporting lightning arresters. This has caused considerable recurrent expense for utilities, particularly where poles exist in remote areas of rough terrain, creating a need for a ground lead disconnect device which will disconnect the ground lead when current flow exceeds a certain level, but which will not result in the ejection of any hot materials which could cause fires.